The tephrochronology and radiocarbon dating of North Atlantic, Late-Quaternary sediments: an example from the St. Kilda Basin

Abstract

Abstract A sequence of disseminated basaltic tephras of Icelandic provenance has been investigated in sediments of Late Quaternary age recovered from the St Kilda Basin, on the Scottish continental shelf. The tephras were deposited from gradually melting rafted pack ice, transported on an anti-clockwise surface current originating to the north of Iceland. The presence of these ice-rafted tephras extends the zone of this current activity well beyond its previously documented western limit, demonstrating current impingement on the UK continental shelf. The evidence of ice-rafting, together with the biostratigraphy and a series of AMS 14 C dates, confirm that this deposition occurred during the Younger Dryas chronozone. Electron probe microanalysis (EPMA) of glass-shard geochemistry is used to ralate the St Kilda tephras to tephras found in marine and terrestrial deposits throughout the North Atlantic area, and to possible volcanic centres in Iceland. The joint role of tephrochronology and radiocarbon dating is discussed in relation to the comparative reliability of marine and terrestrial timescales. Problems with the chronology of the terrestrial equivalents of these tephras in Northern Iceland are highlighted.